The present invention relates to crystalline gatifloxacin pentahydrate and a process for producing it.
Gatifloxacin, chemically 1-cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-(3-methyl-1piperizinyl)-4-oxo-3-quinolinecarboxylic acid, is represented by the following structure: 
Gatifloxacin is a broad-spectrum quinolone antibiotic which is disclosed and claimed in U.S. Pat. No. 5,043,450 as being isolated as the hemihydrate. U.S. Pat. No. 5,880,283 discloses a sesquihydrate crystalline form of gatifoxacin that is disclosed as having advantages over the hemihydrate in pharmaceutical manufacturing. Such advantageous properties for the sesquihydrate in comparison to the hemihydrate include enhanced stability under varying conditions of humidity and superior disintegration and dissolution rates of tablets made therefrom.
Both the hemihydrate and the sesquihydrate forms have demonstrated a definite tendency to form higher hydrates in the presence of water.
In accordance with the present invention, it has been found that gatifloxacin pentahydrate in highly homogeneous form is advantageous to previously known forms and can be utilized to prepare stable pharmaceutical dosage forms, including an aqueous suspension, because it is the most physically stable form and does not have a tendency over time to convert to another crystalline form.